[brucepick]

What I like is that promoting it gets people thinking about aero.

But I suspect the design won't help. It's a no-brainer that you'd save more by driving 65 instead of 75 and leave the license plate cover off the car. 60, even better.

To go on the front of the car I say it should be a rounded bulge just like most modern cars noses.

For the back, maybe tapering to a point but I don't think it should be concave like the photo shows. However for the back, I kinda think it might have to match the width/height of the car's rear face to really do much. Much bigger than a license plate cover.